3. A ball of mass m moves in a vertical circle at the end of a string.By how much is the tension at
問題詳情
3. A ball of mass m moves in a vertical circle at the end of a string.By how much is the tension at the bottom greater than that at the top? (A)0； (B) 2 mg； (C) 4 mg； (D) 6mg； (E) None.